Method for contacting vapors or gases with finely divided contact materials



1945- N. E. PEERY METHOD FOR CONTACTING VAPORS 0R GASES WITH FINELYDIVIDED CONTACT MATERIALS Filed Nov. 6, 1944 lnven rorz Norm an E. PeecgPatented a. 2, 1945 UNITED STATES PATENT OFFICE METHOD FOR corir 'znvoVAPOBS OB GASES WITH MATERIALS FINELY DIVIDED CONTACT ApplicationNovember 6, 1944, Serial No. 562,164

8 Claims. (Cl. 198-52) This invention relates to an improved method forthe contacting of gases or vapors with finely divided solid catalysts orother contact agents.

A particular embodiment of the invention relates conversions .andtreatments which are accelerated by contacting the material to beconverted or treated in the vapor state with solid catalysts or othercontact agents under suitable conditions. In many cases the solidcontact agent is employed in the form of pellets or other relativelylarge lumps of pieces and remains in a relatively fixed position withrespect to the material contacted therewith. It is generally recognized,however,

- that in most cases, by the use of a suitable system,

the treatment or conversion can be carried out with the contact agent ina finely divided state, and that,-in general, several distinctadvantages canbe gained in so doing. with these advantages inmind,.considerable attention has been given,

particularly in the past several years, to the development of varioussystems for the application of finely divided contact agents. As aresult, a considerable-number of systems and modifications have beensuggested. The variou sytems proposed may be classified into a fewdistinct types according to whether the treatment is car ried out intubes or chambers, whether the con tact agent is transportedmith thereactant vapors or falls countercurrent thereto, and whether the contactagent is employed in a dense or freely suspended state. The type ofsystem found to be best for most general application and adopted by theindustry is that type in which the finely divided contact agent isemployed in a pseudoliquid or fluidized state. The process of theinventionis of this type.

Dry, non-sticky solids, when in a suitable state of subdivision, may bemade to exist in three distinct states. (1) If allowed to settle inbulk, they form a hard micro-porous solid mass which may be friable, butis usually difllcult to return to the original finely divided stateexcept by grinding. (2) If mixed with a suflicient quantity of agitatedgas or vapor, the individual particles are uniformly dispersed andsuspended in the gas or vapor. In this state the mixture may becompressed or expanded and the solid may be .considered as being in apseudo gaseous state. (3) If aerated with a limited amount of gas orvapor they .exist in a pseudo-liquid or fluidized state. When in thefluidized state they behave'in most respects as a liquid. Thus. theyfiowtreely: they may. be pumped like a liquid; like a liquid they forman interface between the pseudo-liquid and pseudo-gas phase: gases maybe bubbled" up through the fluidized phase much as with a true liquid.Thus, if a quantity of a finely divided solid contact agent, forinstance a powder passing a mesh screen, is allowed to stand in areactor or other vessel with no injection of gas it will settle into adense relatively hard mass. If. on the other hand, a controlled amountof gas is injected into the bottom of the vessel the finely dividedsolid will be maintained in the pseudoliquid state, Ifthe quantity ofgas injected is gradually increased, it is found that the density of thepseudo-liquid or fluidized solid gradually decreases while the densityof the gas phase above the pseudo-liquid gradually increases until apoint is reached at which a small increase in the amount of gas addedcauses a great increase in the density of the upper gas phase and thewhole or a good portion or the solid becomes freely suspended in thegas. This behavior is analogous to the behavior of a liquid inequilibrium with its vapors under constant pressure when the temperatureis increased, the gas velocity corresponding to the temperature and thecritical gas velocity corresponding approximately to the criticaltemperature. The gas velocity at this point,

hereinafter called the critical velocity, depends upon the physicalproperties of the particular solid and the viscosity of the gas. In thecase of the finely divided synthetic silica-alumina catalysts forexample, the critical velocity is in the order of 1.5 to 3 feet persecond calculated for the same conditions but with the catalyst absent.The density of the fluidized catalyst corresponding to the critical gasvelocity as hereinbefore defined, is hereinafter referred to as thecritical density.

One of the first commercial applications of finely divided contactagents in a fluidized state generator respectively. The up-fiow hinderedsettling reactor consists essentially of a vertically.

tively large amount of catalyst must'he carried overhead (usually from 1to poundsof catalyst per pound of oil) the density oft he exitsuspension must be relatively high (compared to bottom-draw-oif systems)and ,the density of the main catalyst mass is fixed at a relatively lowvalue. This condition is diilicult to maintain constant. Thus if thevelocity is allowed to decrease slightly the density of the efliuentdecreases markedly, the density off the main catalyst mass increases andremains in a fluidized state and little or no catalyst is withdrawnuntil the reactor overflows; if the velocity is allowed to increaseslightly the rate of catalyst carry-over is greatly increased,

the density of the main catalyst mass decreases,

. and the reactor is largely depleted of catalyst.

Another disadvantage of this system is that it allows catalystsegregation to take place. Thus, there is a considerable tendency forthe smaller catalyst particles (fines) to pass through the reactorquickly leaving the coarser particles to remain in the reactor forconsiderable periods of time.

More recent plants are provided with so-called bottom-draw-oif reactorsand regenerators. The bottom-draw-ofi reactor has several advantagesover the up-fiow hindered settling reactor and is considered to be asubstantial improvement. In the bottom-draw-ofi. reactor the vaporscarrying finely divided catalyst in suspension are introduced at or nearthe bottom as before. The partially spent catalyst is continuouslyremoved from the bottom of the reactor through a standpipe (catastat).Since the catalyst is removed from the bottom instead of the top thevapor velocity in the reactor is, not critical and may be adjusted at a.safe rate well below the critical velocity. This allows a much greaterflexibility and ease of control. Likewise the difiiculty due tosegregation is entirely eliminated. A most important advantage, however,is that it allows a more dense fluidized bed of catalyst to be used.Since the activity or eefictiveness of the catalyst is proportional tothe amount of available catalytic surface in the reactor and this inturn is proportional to weight of catalyst in the reactor, it is evidentthat by doubling the density of the catalyst bed the efficiency of theprocess may be doubled. This direct ratio of improvement is not obtainedhowever with bottom draw-oil reactors because of certain other defectsor disadvantages inherent in the bottom draw-off system. A primarydisadvantage of the bottom draw-oil reactors is that, the inlet forfresh catalyst and the outlet for spent catalyst being both at or nearthe bottom, a considerable amount of the fresh catalyst introduced isimmediately withdrawn without being properly used. This .is referred toas by-passing. Another disadvantage is that the free space above thelevel of the fluidized catalyst (disengaging space) is relatively freeof catalyst (density less than about 0.5 pound per cubic foot) Incatalytic cracking this allows a certain amount of undesired thermalreaction to take place in the disengaging space. In catalystregeneration it makes the very undesirable phenomenaknown asafter-burning! diflicult to pre-' vent or control.

In the method of the present invention the gas or vapor is contactedwith the finely divided contact material in such a manner that therespective advantages of both the up-fiow hindered settling reactor andthe bottom draw-oft fiuid catalyst reactor are realized without theirattendant disadvantages. This is accomplished by contacting the finelydivided contact agent at two separate and distinct vapor velocities andcatalyst densities as hereinafter described. The principles of theinvention may most conveniently be explained in connection with atypical operation. To assist in the description reference is had to theattached drawing wherein there is shown by means of diagrammaticfigures, not drawn to scale, the more important apparatus and flows in atypical system adapted for the continuous operation and continuousregeneration of the finely divided catalyst according to the'method oithe invention. The system illustrated is adapted for carrying outvarious catalytic conversions and/or treatments with various finelydivided solid contact agents. However, for the purpose of thedescription the catalytic cracking of a hydrocarbon oil with a finelydivided clay-type cracking catalyst will be used as a typical example.

Referring to the drawing, the hydrocarbon oil to be cracked, forinstance a gas oil, is preheated and vaporized by means not shown andthe vapors are charged to the system via line I. The vapor picks up adesired amount of hot freshly regenerated catalyst from the standpipe 2.The

amount of catalyst added is usually within the range of from about 3pounds to about 25 pounds per pound of oil and is controlled by suitableslide valves 3. The oil vapors carrying the suspended catalyst enter thebottom of the reactor 4 and are distributed by a suitable distributingmanifold 5. The reactor 4 is essentially an elongated chambear of suchcross section that the desired plant capacity may be obtained withoutexceeding the critical vapor velocity. In operation a substantial bed ofthe finely divided catalyst is maintained in the lower half of thereactor. The height of the catalyst bed is adjusted to afiord thedesired space velocity and normally extends up to at least the height ofthe manifold 6. The bed of finely divided catalyst is maintained in apseudo liquid state by the vapors {introduced at the bottom. The densityof the fluidized bed is relatively high and is above the criticaldensity.

In order to maintain a desired depth of catalyst bed and to effectwithdrawal of the partially spent catalyst the vapor velocity in. theupper section of the reactor is increased to exceed the criticalvelocity. The increase in the vapor velocity obtained by the injectioninto the reactor of a second portion of gas or'vapor via manifold 6. Inthe system illustrated, the gas; added isa recycled portion of theproduct gass? Th mixture of product vapors, partially spent catalyst andadded gas leaves the reactor at the top via line I and passes to asuitable cyclone separator 8 wherein the partially spent finely dividedcatalyst is separated. The mixture of product vapors and recycled gaspasses via line 9 to a fractionator Ill. Cycle oil or heavy residue isremoved from the bottom of the fractionator via line H. The gasoline andgaseous products are removed from the fractionator via line l2 and afterbeing cooled in a condenser l3 are passed to a separator l4.Gasinvention. For instance, the process may be ap- II and line It. Thegaseous product from the separator consists largely of hydrocarbon gaseshaving 4 or less carbon atoms. a portion ofthis generator or by anyother means. It is however preferably regenerated using the principlesjust described. Thus the partially spent catalyst is picked up andcarried by a stream of air via line 22 to the bottom of the regenerator22 where it is injected into the bottom of a fluidized bed of thecatalyst undergoing regeneration. As before, the. fluidized bed ismaintained at a relatively high density above the critical density bycontrol of the air flow. An additional quantity of gas, which in thecase illustrated is recycled flue gas, is introduced at about midway inthe regeneraior by the manifold 24. The amount of gas added, as before,is adjusted to give a gas velocity in the upper section of theregenerator above the critical velocity. The regenerated catalyst iscarried with the mixed gas stream out from the top of the regenerator toa suitable cyclone separator 25. The regenerated catalyst is recycled tothe reactor as described via standpipe 2. The hot spent regeneration gasis passed through a waste heat boiler 26. A portion of the partiallycooled gas is recycled to the regenerator 23 via pump 21, line 2| andmanifold 24. The remainder is withdrawn from the system via line 29.

It will be apparent that the above-described typical operation may bemodified in certain respects while still retaining the principles of theplied for other conversions than catalytic cracking; various otherfinely divided solid catalysts may be used in place of the clay-typecatalysts and the gas or vapor injected via manifolds 8 and/or 24 may beany suitable material other than the particular products shown. On theother hand essential features of the invention are: (1) that the finelydivided contact agent enters the reactor or regenerator at or near thebottom and is withdrawn with the gas or vapor from the top, (2) that theamounts of gas or vapor introduced with the catalyst at the bottom areinsufllcient to exceed the critical velocity, thereby maintaining adefinite bed of relatively dense fluidized catalyst in the lower sectionof the contactor, and, (3) that a second portion of gas or vapor isintroduced between the bottom and the top of the contactor in such anamount that the velocity or the combined vapors or gases exceeds thecritical velocity.

I claim as my invention:

1. Method for continuously contacting a gas or vapor with a recycledfinely divided contact agent which comprises injecting near the bottomof a bed of said finely divided contact agent a mixture of said gas orvapor and said finely divided contact agent, the rate of flow of saidgas or vapor being adjusted to maintain said bed of finely dividedcontact agent in a relatively dense pseudo-liquid state, and injectingat a point substantially at the top of said bed a gas or vapor at such arate that the velocity of the combined gas or vapor exceeds thecriticalvelocity corresponding to said pseudoliquid state, thereby to produceand maintain a free suspension or gaseous phase above said point ofinjection and to remove in suspension from thewofsaidbedaquantityofsaidfinsly divided contact .agent substantially equvalent to the amount of said finely divided contact agent lniected nearthe bottom.

2. Method for continuously contacting a gas or vapor with a cycledfinely divided clay-type catalyst which comprises injecting near thebottom of a bed of said finely divided clay-type catalyst a mixture ofsaid gas or vapor and said finely divided catalyst, the rate of fiow ofsaid gas or vapor being adjusted to maintain said bed of finely dividedcatalyst in a relatively dense p eudo-liquid state, and injecting at apoint substantially at the top of said bed a gas or vapor at such a ratethat the velocity of the combined as or vapor exceeds the criticalvelocity corresponding to said pseudo-liquid state, thereby to produceand maintain a free suspension or gaseous phase above said point ofinjection and to remove in suspension from the top of said bed aquantity of said finely divided catalyst sub- L stantially equivalent tothe amount of said finely divided catalyst injected near the bottom.

3. Method for the treatment of a hydrocarbon oil with a cycled finelydivided clay-type catalyst which comprises injecting near the bottom ofa bed of said finely divided catalyst a mixture ous phase above saidpoint of injection and to remove in suspension from thetop of said bed aquantity of said finely divided catalyst substantially equivalent to theamount of said finely divided catalyst injected near the bottom.

4. Process according to claim 3 in which the gas or vapor injected nearthe top of the bed is a normally gaseous hydrocarbon fraction.

5. Prbcess according to claim 3 in which the gas or vapor injected nearthe top of the bed is a recycled gaseous fraction of the product of theprocess.

6. Method for continuously contacting a gas or vapor with a recycledfinely divided contact agent which comprises injecting near the bottomof a bed of said finely dividedcontact agent a mixture of said gas orvapor and said finely divided contact agent, the rateof flow of said gasor vapor being adjusted to maintain said bed of finely divided contactagent in a relatively dense pseudo-liquid state, and injecting at apoint substantially at the top of said bed a recycled portion ofpreviously contacted gas or vapor at such a rate that the velocity ofthe combined gas or vapor exceeds the critical velocity corresponding tosaid pseudo-liquid state,

, thereby to produce and maintain a free suspension or gaseous phaseabove said point of injection and to remove in suspension from the topof said bed a quantity of said finely divided contact agentsubstantially equivalent to the amount or said finely divided contactagent injected near at the top of said bed a recycled gas obtained ashereinafter specified at such a rate that the velocity of the combinedgas and vapor exceeds the critical velocity corresponding to saidfluidized state, thereby to produce and maintain a free suspension orgaseous phase above said point 10 of injection and to remove insuspension from the top of said bed a quantity 01 said finely dividedcatalyst substantially equivalent to the amount of said finely dividedcatalyst continuously supplied to said bed, separating finely 15 dividedcatalyst from the suspension, separating a gaseous fraction from theproduct, and re- 8. Method for the regeneration of a partially g9 spentfinely divided contact agent air which comprises injecting near thebottom of a bed or said finely divided contact agent maintained underregeneration conditions a mixture of air and said partially spent finelydivided contact agent, the rate of flow of air being adjusted tomaintain said bed of finely divided contact agent ,in a relatively densefluidized state, and injecting at a point substantially at the top ofsaid bed, a recycled portion of spent regeneration gas at such a ratethat the velocity of thecombined gases exceeds the critical velocitycorresponding to said fluidized state, thereby to produce and maintain afree suspension or gaseous phase above said point of injection and toremove in suspension from the top of said bed a quantity oi regeneratedfinely divided contact agent substantially 7 equivalent to the amount ofsaid finely divided contact agent continuously supplied to said bed.

NORMAN E. PEERY.

